I found this guy on YouTube, his juggling tutorials seem very straight forward and clear. Of course I'm still doing the basics (as in this video), but he's got lots of more advanced tricks and stuff, so I suggest you take a look at them if you're interested in learning more. The description to the video is essential though, so I'll copy it here:

DescriptionX

Step 1
Throw one ball to your other hand. Whilst this ball in the air, wait until it reaches its maximum height and then, throw the second ball. Make sure you catch both balls in opposite hands and do not pass the balls along, throw them.

Step 2
Opposite side of step 1.

Step 3
The same process as steps 1 and 2 however, now you have an extra ball in your hand, you can continue the pattern for 1 extra throw. Do continous throws for the 3 ball pattern.

Step 4
Opposite side of step 3.

All Together
Now, if you think about it steps 3 and 4 can be made continuous as you end up in your original position. Simply continue juggling the exchanges for the 3 ball cascade!

PlayPoi has all the information you need to know about poi, as well as very good tutorials called Poi Basics. There are six videos going from the complete basics up to fairly advanced techniques, all explained in a very simple, straight-forward manner (or at least I thought so).

Firetoys has a really great variety of toys, not only fire stuff, I've bought things from them a couple of times and it's always been really good. UK based.

Oddballs is the juggling store in Camden, London. Their website also has a really good selection of all kinds of toys, I've also bought from them and can recommend them. If you're in London, they also run a weekly juggling meeting not far from the store. UK based.

Flowtoys specializes in glowing toys and people keep telling me they're really good, though I've not bought stuff from them personally. California based.